Buenos Aires: Argentina's River Plate has threatened Bayer Leverkusen after the German league side put striker Lucas Alario through a medical examination without his club's consent.

File image of Lucas Alario. Reuters

Leverkusen want to sign Argentina international Alario, who has scored 41 goals in 82 games and won four trophies with River Plate, to replace Mexico striker Javier Hernandez after 'Chicharito' joined West Ham.

The German club has landed in hot water because they "violated ethical rules, especially FIFA's regulations" by approaching Alario without asking for Plate's permission, according to the Argentinian club.

"In the event that you do not put out a statement distancing yourself from a transfer within the next 24 hours, we will take the matter to FIFA," Plate wrote in a three-page letter addressed to Leverkusen's CEO Michael Schade.

Copies were also sent to European football's governing body UEFA, the German Football Association (DFB) and world football's governing body FIFA.

According to reports, Plate only learnt Alario was to undergo a medical in Buenos Aires by Leverkusen's team doctor Karl Dittmar through the Argentinian media.

Under FIFA regulations, a contract can not be cancelled by only one party when a season is already underway and Argentina's First Division started last weekend.

Media in Argentina reported a week ago that Leverkusen had submitted an offer of 16 million euros ($19.2m), but Plate are accusing the Germans of inciting Alario to a breach of contract.